Moving Attic duct work to conditioned space to save energy. Return on Investment?

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Instead of foaming the entire roof deck I'm going to ask a contractor to just frame around the HVAC unit with 2x4's and use regular fiberglass batts, to basically make a mini conditioned room around it. Hopefully in a manner that can be taken out easily when the furnace is replaced latter in life. Maybe using 2" foam would work better for that reason.

Obviously the furnace is going to need an air supply for burning, so a new 3' long duct will be needed from the furnace to the outside enclosed wall.

Can this duct be closed off during the summer when the furnance is obviously not running? Obviously if someone forgets to remove it before turning on the heat it will not be good!

I think that is about the best I can do to bring everything into conditioned space short of ripping the old system out and redoing it.

Thoughts on why installers are telling me this is not worthwhile, yet everything I read says it is? Who's right?
Because we are all creatures of HABIT. It is what we always do!!!! To think otherwise would call into question our idea of "best practices"
The main change for the latest Ed of Man J was it's attention to duct energy losses.

2 thoughts first, you need a trunk and branch duct system not that spaghetti system with 2x the surface area AND
I think it would be easier to install some "knee walls" that would more effectively get a good deal of your equipment and duct inside the thermal envelope.
THere is not a lot of leakage with that flex but I think you could see a 1/3 reduction SWAG

You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

instead of building a box around equipment, adding make up air for furnace in box,
bringing some ducts into living space and worrying about closing off make up air for
furnace in a box...(which you wouldn't have to worry about in the summer fyi)..
you need to put pen to paper and estimate what ball park costs this would require.

materials, labor, pita factor working in attic, sheetrock finishing for cathedral,
painting..adds up to quite a bit to me and I'm a diy person.(except sheetrock finishing)

then the problem of finding someone to competently do the work.

I'm all for ductwork inside living space. but all of the duct work, all plenums
and all returns. all equipment.
but this isn't your set up.
no common area to feed all ducts to all rooms inside the living space.

say you decide to foam insulate the attic..still you have work to do.
finding a competent installer.
removing insulation in attic at minimum
3" from eaves of house.
moving junk out of attic.
venting bath fans, stove, adding a duct for make up air for furnace
and gas water heater if w/h is in attic.
all prior to the foam install.

granted your duct layout is crap. I think we all agree on that one.
and like Genduct says..flex is less leakage than hard pipe.
I would add that you still have to mastic seal duct take offs at plenum.
plenums to equipment, return air and each supply box where it enters
house & supply grill is attached. flex duct leaks at each end. depending
on the care that was used to cut holes in supply plenum, duct leakage
varies.

so add up costs for foam & venting, make up air & duct sealing.

compare the costs of option 1 (equipment in a box etc) to option
2 (foam etc).

how high are your utility costs now?
have you been in the house a full heating and cooling season?
comfort issues? hot rooms, cold spots..allergies?

I can't say that I'd spend time building box for furnace and furring down
cathedral for one duct.

best of luck.

The cure of the part should not be attempted without the cure of the whole. ~Plato

I agree, Air sealing and insulating in its self will give you great results.Build a insulated room around the equipment in the attic ive seen done before. redesign the whole house is not needed un less your duct were undersized and you have bad static pressure.

Originally Posted by jtrammel

I really don't think you would save much by moving the duct inside. If you moved all of it and the furnace/coil yes but not just some of the lines. The duct system could be designed much better and wrapped with r8 insulation but the biggest savings will be air sealing the ductwork. Then foaming the roof deck or air sealing the attic floor and better insulating the attic floor and ductwork and adding a radiant barrier to roof deck.

Here are some photos of the main trunk being furred down with framing. The left hand side, has a boxy room sticking out. Ontop of that is the old distribution box which will feed the bathroom beneath it, and two 6" flex tubes will continue to the two bedroom closets and exhaust in the actual bedrooms.

I have a general contractor friend that is doing the labor. Material costs are around $1,000. I figgure if I save $30 a month break even will be around 3 years. I did find two ducts in the attic that did not even have a zip tie securing them to the ceiling register, just pressure fit.

If I were to do it again I would of NOT furred down the main cathedral ceiling and just had a huge exposed duct work trunk.
second photo is of hole in bathroom ceiling.
last photo is of furred down bathroom ceiling.

In the photo where flex exits fur down over bath bump-out, I would advise a 90° round sheetmetal elbow be used there vs. just bending the flex to make the turn downward. Flex duct may be indeed flexible, but it doesn't do 90 degree turns very well. Tends to retrict air movement, as about the only way you'll get a sharp 90 with flex in that situation is to kink it.